Do all Travco's have exact date of manufacture on beam?

[Zed]

So my travco has 9-16-71 hand written in grease pen or something on the back bolt on plate, the removable one between the frame rails and the rear bumper. You have to take it off to see it. \n\nI'm guessing thats what the date is since mine is a 71. Just curious if everyone's has the date of manufacture here. Mine is very legible. \n\nI wish I'd taken a picture and if I have to pull it off again I will next time.